Sweet violet has a long and proven history of folk use, especially in the treatment of cancer and whooping cough. It also contains salicylic acid, which is used to make aspirin. It is therefore effective in the treatment of headaches, migraine and insomnia. The whole plant is anti-inflammatory, diaphoretic, diuretic, emollient, expectorant, and laxative. It is taken internally in the treatment of bronchitis, respiratory catarrh, coughs, asthma, and cancer of the breast, lungs or digestive tract. Externally, it is used to treat mouth and throat infections. The plant can either be used fresh, or harvested when it comes into flower and then be dried for later use. The flowers are demulcent and emollient. They are used in the treatment of biliousness and lung troubles. The petals are made into a syrup and used in the treatment of infantile disorders. The roots is a much stronger expectorant than other parts of the plant but they also contain the alkaloid violine which at higher doses is strongly emetic and purgative. They are gathered in the autumn and dried for later use. The seeds are diuretic and purgative. They have been used in the treatment of urinary complaints are considered to be a good remedy for gravel. A homeopathic remedy is made from the whole fresh plant. It is considered useful in the treatment of spasmodic coughs and rheumatism of the wrist. An essential oil from the flowers is used in aromatherapy in the treatment of bronchial complaints, exhaustion and skin complaints. Source: https://pfaf.org/
Find more about this plant on Wikipedia.